A conventional writing tool, for example, as shown in FIG. 8, and FIGS. 9(a) and (b), has a rotation cam mechanism for projecting the tip of a refill for a ball-point pen out of, or retract it into the head member (not shown) of the writing tool, which comprises cam body 1 attached on the inside of the rear portion of outer sleeve 10 connected with the head member, rotation cam 2 engaged with cam body 1 or released from cam body 1, and cam bar 3 for pushing rotation cam 2. Refill 5 for a ball-point pen is inserted into outer sleeve 10. A return spring (not shown) is provided between a step-shaped bearing portion (not shown) formed on the inside of the head member and a bearing portion (not shown) of refill 5 for retracting ball-point pen refill 5.
Cam body 1 has some, say three, axial projecting strips 25 arranged at regular angular intervals on the inside thereof, each projecting strip 25 having a shallow groove 26a shaped and having a root 27 at an edge thereof. Deep grooves 26b are formed between respective projecting strips 25.
Ball-point pen refill 5 has rotation cam 2 fitted in a rear portion thereof. Rotation cam 2 has on the outside thereof three axial projecting strips 34 which fit in deep grooves 26b of cam body 1. Strips 34 are made to form a crown which has peaks 35 and roots 36 alternately on an end of the cylindrical portion of rotation cam 2.
Cam bar 3 has six axial strips 30 on an outside thereof, which are fitted into deep grooves 26b of cam body 1. Strips 30 are made to form a crown which has peaks 31 and roots 32 on an end of the cylindrical portion of cam body 1. Cam bar 2 projects out of the rear end of outer sleeve 10.
Cam bar 3 can be pressed in opposition to the return spring. Rotation cam 2 and ball-point pen refill 5, then, can be pressed in opposition to the return spring where the slopes of peaks 35 of rotation cam 2 are fitted to, but deviated a little from, slopes of peaks 31 of cam bar 3. Strips 34 of rotation cam 2 fit into deep grooves 26b of cam body 1 (FIG. 9(a)). Stripes 34 of rotation cam 2, then, can be detached from deep grooves 26b of cam body 1 as follows. In the state shown in FIG. 9(b), the return spring presses the slopes of peaks 35 of rotation cam 2 to the slopes of peaks 31 of cam bar 3. This can revolve rotation cam 2 to make respective peaks 35 fit into respective roots 32. In turn, the slopes of peaks 35 of rotation cam 2 press the slopes of roots 27 of cam body 1 to further revolve rotation cam 2. The respective peaks 35 of the cylindrical cam 2, then can fit with respective roots 27 of cam body 1 as shown in FIG. 9( b). The tip of ball-point pen refill 5, thus, can be held projected out of the head member.
In the state shown in FIG. 9(b), when cam bar 3 is pressed again in opposition to the return spring, rotation cam 2 and ball-point pen refill 5 can be pressed in opposition to the return spring where the slopes of respective peaks 35 of rotation cam 2 are fitted to, but deviated a little from, the slopes of respective peaks 31 of cam bar 3. This detaches peaks 35 of rotation cam 2 to allow turning, which in turn allows peaks 35 and roots 36 of rotation cam 2 to fit respective peaks 31 and roots 32 of cam bar 3. In turn, the force of the return spring makes the slopes of peaks 35 of rotation cam 2 press the slopes of respective roots 27 of cam body 1 to turn rotation cam 2. The strips 34 of rotation cam 2, then, can be pressed in the respective grooves 26b of cam body 1 as shown in FIG. 9(a). This allows cam bar 3 to be retracted. At the same time, the tip of ball-point pen refill 5 is drawn into the head member.
However, since the cam mechanism is mounted in the rear portion of the outer sleeve, the length of a writing tool is long, therefore it is impossible to form compact small writing tools. Further it is impossible to form writing tools having two head members which are attached to both ends of an outer sleeve in which it is possible to project the tips of refills out of or retract them into both head members.